System and method for water pasteurization and power generation

ABSTRACT

A system and method for creating power and pasteurizing water is provided. The system includes a power generation subsystem and a water pasteurization subsystem, which are linked together as follows. The power generation subsystem comprises a turbine power generator. Air (or other suitable working fluid) flows through the turbine power generator to generate power by known methods. The air is heated prior to flowing into the turbine to increase its speed for greater power generation. The water pasteurization subsystem includes one or more heat exchangers, at least one of which is connected to receive the hot airflow exiting the turbine. The heat from the turbine-exiting airflow is utilized for pasteurizing colder wastewater inside the heat exchanger.

[0001] CLAIM FOR PRIORITY

[0002] This application claims priority to U.S. Provisional PatentApplication Serial No. 60/427,069, filed Nov. 18, 2002. This applicationalso claims priority to a U.S. provisional patent application filed Oct.8, 2003, entitled “SYSTEM AND METHOD FOR WATER PASTEURIZATION AND POWERGENERATION,” under attorney docket number GREGR.001PR2, for which aPTO-assigned application number is not available at the present time.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates generally to water purification,and specifically to water pasteurization and turbine power generation.

[0005] 2. Description of the Related Art

[0006] Traditional methods for purifying wastewater includechlorination, exposure to ultraviolet (UV) radiation, and ultrafiltration. Unfortunately, there are drawbacks to each of these methods.

[0007] Chlorination involves the treatment of water with chlorine or achlorine compound. If the chlorine concentration is great enough, thetreated water tends to smell and taste bad. Some people object to thesmell and taste of very small amounts of chlorine. In addition,chlorination can be harmful to people's health. If water suppliescontain humic compounds, which form as a part of the decomposition oforganic materials such as leaves, grass, wood, or animal wastes,chlorination of such water can produce trihalomethanes (THMs). BecauseTHMs are very seldom associated with groundwater, they are primarily aconcern when surface water supplies are used. Lifetime consumption ofwater supplies with THMs at a lever greater than 0.10 milligrams perliter is considered by the Environmental Protection Agency to be apotential cause of cancer.

[0008] Treatment of water by exposure to ultraviolet radiation iscomplicated and maintenance intensive. It involves the use of UV lamps,which must be replaced periodically. UV treatment also often utilizesreflectors for focusing the UV light toward the water. Such reflectorsmust be cleaned from time to time. Also, it is generally desirable forthe water flow through the UV treatment chambers to be laminar, topromote uniformity of UV exposure. This requires the use of baffles andspecially designed treatment chambers, which increases costs.

[0009] Filtration involves causing the water to flow through a series offilters. Like UV treatment, filtration is maintenance intensive. Thefilters must be cleaned and/or replaced periodically. Further,filtration is often a slow process.

[0010] Pasteurization is yet another known method for purifying water.It involves heating water to a temperature of at least 150-170° F.Pasteurization is typically conducted at low water volumes, such as incampsites and other remote, rural locations. Small, portable solar waterpasteurization units, or solar cookers, are sometimes used forpasteurizing water from solar heat. Generally, pasteurization is notused for large-scale water treatment due to the high costs associatedwith heating large amounts of water.

SUMMARY OF THE INVENTION

[0011] The preferred embodiments of the present invention recognize anew opportunity for synthesis between previously disparately conductedmethods of power generation and water pasteurization. The illustratedembodiment utilizes the heat exhaust from turbine power generation topasteurize large amounts of water.

[0012] In one aspect, the present invention provides a system forproducing power and pasteurizing water, comprising a turbine, a powergenerator, a heat exchanger, and a heat source. The turbine isconfigured to receive a flow of a working fluid, and the working fluidflow is configured to rotate blades and an output shaft of the turbine.The power generator is coupled to the turbine output shaft andconfigured to convert rotation of the output shaft into power. The heatexchanger has first and second internal chambers. The first chamber isconfigured to receive working fluid exiting the turbine, while thesecond chamber is configured to receive water, such as untreated or evenpartially heated wastewater from a municipal wastewater reservoir. Thechambers of the heat exchanger are configured to permit heat exchangebetween working fluid within the first chamber and water within thesecond chamber. Heat flows from the hot working fluid to thecomparatively cold water to preferably raise the water temperature to atleast a water pasteurization temperature. The heat source is configuredto impart heat to working fluid flowing through the turbine and thefirst chamber of the heat exchanger. Typically, the heat source impartsheat to the working fluid upstream of the heat exchanger. In a preferredembodiment, the heat source imparts heat to the working fluid bothupstream and downstream of the turbine.

[0013] In another aspect, the present invention provides a system forproducing electric power and pasteurizing water, comprising a turbinepower generator and a heat exchanger. The turbine power generator isconfigured to convert a flow of working fluid into electric power. Theheat exchanger has first and second fluidly separate internal chambers.As used herein, “fluidly separate” chambers refers to chambersconfigured so that fluids within the chambers are not permitted to mixtogether. The first internal chamber is configured to receive an exhaustflow of working fluid from the turbine generator, while the secondinternal chamber is configured to receive water. The chambers areconfigured to permit heat exchange between working fluid within thefirst chamber and water within the second chamber, to preferablypasteurize water within the second chamber. In a narrower aspect, thesystem further comprises a heat source configured to impart heat toworking fluid flowing into the turbine generator.

[0014] In yet another aspect, the present invention provides a method ofproducing power and pasteurizing water. A working fluid (in theillustrated embodiment, air) is caused to flow through a turbine powergenerator. The flow of working fluid causes the turbine power generatorto generate power. After the working fluid exits the turbine powergenerator, the working fluid is directed into a first of two fluidlyseparate internal chambers of a heat exchanger. The chambers areconfigured to permit heat exchange between the working fluid within thefirst chamber and water within a second of the two chambers. The workingfluid within the first chamber is at a temperature greater than a waterpasteurization temperature. Water is caused to flow through the secondchamber of the heat exchanger, the water initially being colder than thewater pasteurization temperature. The water flowing through the secondchamber is permitted to absorb heat from the working fluid within thefirst chamber. The flow rate of the water flowing through the secondchamber of the heat exchanger is controlled so that the watertemperature rises to the pasteurization temperature.

[0015] In yet another aspect, the present invention provides a method ofproducing electric power and pasteurizing water. Air is pumped through aturbine power generator. The air causes the turbine power generator togenerate electric power. After the air exits the turbine powergenerator, heat is transferred from the air to water, to raise the watertemperature to at least a water pasteurization temperature.

[0016] For purposes of summarizing the invention and the advantagesachieved over the prior art, certain objects and advantages of theinvention have been described above and as further described below. Ofcourse, it is to be understood that not necessarily all such objects oradvantages may be achieved in accordance with any particular embodimentof the invention. Thus, for example, those skilled in the art willrecognize that the invention may be embodied or carried out in a mannerthat achieves or optimizes one advantage or group of advantages astaught herein without necessarily achieving other objects or advantagesas may be taught or suggested herein.

[0017] All of these embodiments are intended to be within the scope ofthe invention herein disclosed. These and other embodiments of thepresent invention will become readily apparent to those skilled in theart from the following detailed description of the preferred embodimentshaving reference to the attached figures, the invention not beinglimited to any particular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a flow diagram illustrating a water pasteurization andpower generation system according to a preferred embodiment of thepresent invention;

[0019]FIG. 2 is a schematic illustration of a heat exchanger used inpreferred embodiments of the present invention;

[0020]FIG. 3 is a flow diagram illustrating an embodiment of theinvention in which digester gas from the wastewater is utilized as anadditional source of heat at the ductburner; and

[0021]FIG. 4 is a flow diagram illustrating an embodiment of theinvention in which digester gas from the wastewater is mixed with thenatural gas fuel source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] A well-known method for producing electric power is to cause afluid, such as steam or air, to flow at high speeds through a turbinepower generator. A turbine power generator typically comprises a turbinecoupled to a power generator. The turbine includes turbine blades and anoutput shaft. The power generator ordinarily includes a shaft that canbe coupled to the turbine output shaft. The generator shaft is equippedwith magnets for converting shaft rotation into electric power.Typically, the working fluid is brought to a superheated gaseous stateto promote higher speed flow through the turbine. The fluid flowsthrough the turbine blades to produce rotation of the turbine andgenerator shafts. The consequent movement of the electromagnetic fieldsof the magnets produces electric current. The generator ordinarilyincludes additional apparatus for capturing and storing the generatedpower. More elaborate apparatus and methods exist for power generation,which are based upon these fundamental principles.

[0023] Preferred embodiments of the present invention utilize the heatof the working fluid after it has exited the turbine power generator topasteurize water. Thus, preferred embodiments of present inventionrecognize an opportunity for synergy between conventional powergeneration and water pasteurization.

[0024]FIG. 1 is a flow diagram illustrating a water pasteurization andpower generation system 5 according to a preferred embodiment of thepresent invention. The system 5 comprises a water pasteurizationsubsystem 6 and a power generation subsystem 8, each identified bydotted lines in FIG. 1. As explained below, the water pasteurizationsubsystem 6 receives wastewater effluent 12 and outputs pasteurizedclean water 30. Simultaneously, the power generation subsystem 8 createselectric power from superheated flow of a working fluid, such as air orwater (but preferably air), through a turbine generator 61.Advantageously, as explained below, the water pasteurization subsystem 6utilizes heat exhaust from the power generation subsystem 8, which is areadily segregated portion of energy from the power generation subsystem8, creating a synergy between the two subsystems.

[0025] This specification begins with a description of the structuralcomponents of the system 5 and follows with an explanation of theoperation of the system.

[0026] The major components of the water pasteurization subsystem 6 area first heat exchanger 16, a second heat exchanger 20, and a residencetank 24. The subsystem 6 also includes a number of flow channels forconnection between these components. The structural configuration of thesubsystem 6 is now explained.

[0027] The first heat exchanger 16 is connected to four water flowchannels as explained below. As used herein, a “flow channel” refers toone or more flow passages or chambers, which can assume any of a largevariety of differing sizes and configurations. The first heat exchanger16 includes two fluidly separate internal chambers. A first chamberserves as a conduit between a wastewater input flow channel 14 and apreheated water flow channel 18, while a second chamber serves as aconduit between a pasteurized water flow channel 26 and a clean wateroutput flow channel 28. Although not shown in FIG. 1, the two chambersof the first heat exchanger 16 are preferably configured, as known inthe heat exchanger art, to enhance heat exchange between fluids withinthe two chambers. Preferably, the two chambers are configured to have alarge surface area of contact with one another to promote greater heattransfer therebetween.

[0028]FIG. 2 is a schematic illustration of a heat exchanger 80appropriate for use with preferred embodiments of the present invention.In particular, the heat exchanger 80 is appropriate for use as the firstheat exchanger 16 and/or the second heat exchanger 20 (described below)shown in FIG. 1, as well as any additional heat exchangers as may bedesired. The heat exchanger 80 includes two fluidly separate internalchambers A and B, with an interface 82 separating the chambers. The heatexchanger 80 includes inlets 84 and 88 and outlets 86 and 90. Thechamber A is connected to the inlet 84 and the outlet 88, while thechamber B is connected to the inlet 88 and the outlet 90. While FIG. 2is shown as a two-dimensional representation, it will be understood thatthe heat exchanger 80 is a three-dimensional structure. As such, thechambers A and B are three-dimensional chambers. While chamber B isshown in two portions, it will be understood that chamber B is onecontiguous chamber, as is chamber A. While the interface 82 of theschematic illustration is shown as two simple linear segments, it willbe understood that the interface 82 is preferably configured to resultin a large surface area of contact between chamber A and chamber B, topromote greater heat transfer therebetween. The two chambers are fluidlyseparate. Thus, a Fluid 1 can flow through chamber A via inlet 84 andoutlet 86 and a Fluid 2 can flow through chamber B via inlet 88 andoutlet 90, without any mixture of the two fluids inside the heatexchanger 80.

[0029] With continued reference to FIG. 1, the second heat exchanger 20is connected to two water flow channels and two airflow channels asexplained below. Like the first heat exchanger 16, the second heatexchanger 20 includes two fluidly separate internal chambers. A firstchamber serves as a conduit between the preheated water flow channel 18and a pasteurized water flow channel 22. A second chamber serves as aconduit between an airflow channel 66 and an airflow emissions channel68. Although not shown, the two chambers of the second heat exchanger 20are preferably configured, as known in the heat exchanger art, toenhance heat exchange between fluids within the two chambers.Preferably, the two chambers are configured to have a large surface areaof contact with one another to promote greater heat transfertherebetween.

[0030] The pasteurized water flow channel 22 serves as a conduit betweenthe second heat exchanger 20 and the residence tank 24. The pasteurizedwater flow channel 26 connects the residence tank 24 to one of theinternal chambers of the first heat exchanger 16, as explained above.One or more of the water flow channels of the pasteurization subsystem 6may be completely or partially insulated to prevent heat loss or gain.In one embodiment, all of the flow channels are insulated. Of course,there is preferably no insulation between the chambers in each of theheat exchangers.

[0031] The major components of the power generation subsystem 8 are afuel source 42 (preferably natural gas), a gas compressor 46, a pump 41,a gas ignition chamber 50, the turbine generator 61, and a ductburner64. The subsystem 8 also includes a number of flow channels forconnection between these components. The structural configuration of thesubsystem 8 is now explained.

[0032] The gas fuel source 42 is connected to the gas compressor 46 andthe ductburner 64 via an uncompressed gas flow channel 44. The gas fuelsource 42 preferably comprises natural gas, such as methane, propane, orbutane, but others are possible. The gas compressor 46 is connected tothe gas ignition chamber 50 via a compressed gas flow channel 48. Thegas ignition chamber 50 is also connected to an airflow channel 52 and aturbine inlet airflow channel 54. In the illustrated embodiment, thepump 41 is provided for pumping air 40 received at a pump inlet 39 intothe airflow channel 52. The gas ignition chamber 50 preferably includesa natural gas igniter (also not shown), such as an electric sparkgenerator, a flame generator, or other like apparatus. The turbine inletairflow channel 54 is connected to an inlet of the turbine generator 61.In the illustrated embodiment, the turbine generator 61 includes aturbine 56 having an output shaft 58 coupled to a power generator 60. Asused herein, a “turbine generator” is a combination of a turbine and apower generator, the turbine output shaft configured to drive thegenerator.

[0033] A fluid output of the turbine 56 is connected to the ductburner64 via an “exhaust” airflow channel 62. The airflow exiting the turbine56 into the airflow channel 62 is sometimes referred to herein as the“turbine exhaust.” The ductburner 64 is also connected to theaforementioned airflow channel 66 that leads to the second heatexchanger 20. The airflow emissions channel 68, which is also connectedto the second heat exchanger 20, leads to a stack 70 for emission of airinto the environment. A continuous emissions monitoring (CEM) system 72,as known in the art, is preferably provided for monitoring the qualityof air in the airflow emissions channel 68. One or more of the airflowchannels of the power generation subsystem 8 may be completely orpartially insulated to prevent heat loss or gain. In one embodiment, allof the flow channels are insulated.

[0034] Now the operation of the entire system 5 will be explained,according to a preferred embodiment of the invention. As mentionedabove, the power generation subsystem 8 converts superheated airflowinto electric power. Air 40 at or near room temperature (e.g., 59° F.)is preferably pumped through the airflow channel 52 into the gasignition chamber 50. Simultaneously, natural gas at approximately 100psig flows from the gas fuel source 42 through the uncompressed gas flowchannel 44 into the gas compressor 46. The compressor 46 compresses thegas to a much higher pressure (e.g., 318 psig), so that the gas, whenignited, will have a greatly increased heat generation capacity. Thepressurized gas flows through the compressed gas flow channel 48 intothe gas ignition chamber 50. In the gas ignition chamber 50, thepressurized natural gas mixes with the air 40. The natural gas ignitionmeans (not shown) ignites the pressurized natural gas in the presence ofthe air 40, releasing a great deal of heat into the air. As a result,the air inside the gas ignition chamber 50 is brought to a superheated,pressurized gaseous state. In this condition, the superheated air(including exhaust fiumes from ignition) flows at high speed through theturbine inlet airflow channel 54 into the turbine 56. The flow ofsuperheated air at high speeds causes the turbine blades to rotate,producing rotation of the output shaft 58. The power generator 60converts this rotation into electricity in the manner explained above.

[0035] After the superheated air flows through the turbine 56, itcontinues through the exhaust airflow channel 62 into the ductburner 64.The ductburner 64 receives natural gas via the uncompressed gas flowchannel 44. In an alternative embodiment, the ductburner 64 may receivecompressed gas flow from the compressed gas flow channel 48. Like thegas ignition chamber 50, the ductburner 64 preferably includes a naturalgas igniter (not shown), such as an electric spark generator, a flamegenerator, or other like apparatus. Inside the ductburner 64, thenatural gas is ignited to impart additional heat to the air as it flowsonward through the airflow channel 66 into one of the two internalchambers of the second heat exchanger 20. It will be understood that theductburner 64, while preferred, is not required. Inside the second heatexchanger 20, the air cools down significantly due to heat exchange withcooler water, as described below. The cooled air exits the second heatexchanger 20 via the airflow emissions channel 68. The cooled air isemitted to the environment through a stack 70.

[0036] In order to comply with emissions standards, the second heatexchanger 20 preferably includes catalysts for cleaning the air beforeit is emitted into the environment via the stack 70. Preferably, aselective catalytic reduction (SCR) catalyst is utilized for reducingnitrogen oxide (Nox) emissions. The SCR catalyst may be used inconjunction with reducing agents, such as ammonia- or urea-basedcompounds. Other catalysts may also be used for complying with emissionsstandards, such as CO catalysts, as known in the art. As mentionedabove, a CEM system 72 is preferably utilized for monitoring the qualityof the air emitted into the environment via the stack 70, to ensurecompliance with emissions standards.

[0037] In operation, the water pasteurization subsystem 6 pasteurizeswastewater effluent 12 by causing the wastewater 12 to flow through theheat exchangers 16 and 20. Before entering the water pasteurizationsubsystem 6, the wastewater effluent 12 is at or near room temperature(e.g. 60-66° F.). The wastewater 12 flows into one of the two internalchambers of the first heat exchanger 16 via the wastewater input flowchannel 14. Although not shown, a pump can be provided to pump thewastewater 12 into the input flow channel 14. Alternatively, thewastewater 12 can flow into the input flow channel 14 by gravity alone,by, for example, a collection tank positioned vertically above the firstheat exchanger 16. In some configurations, filters can be provided tofilter out larger debris from the wastewater 12 before it flows into thefirst heat exchanger 16.

[0038] It will be understood that there may be other structures andsystems for transferring heat from turbine exhaust to unpasteurizedwastewater. For example, there may alternatively be provided a closedcirculating fluid system for transferring heat from the turbine exhaustinside the second heat exchanger 20 to the wastewater inside the firstheat exchanger 16. Other heat exchanging structures and systems are alsopossible.

[0039] Inside one of the two internal chambers of the first heatexchanger 16, the wastewater absorbs heat from hot, pasteurized waterinside the other of the two chambers (explained below). This raises thetemperature of the wastewater to a pasteurization or near-pasteurizationlevel (e.g., preferably at least 130° F., more preferably at least 135°F., and even more preferably 140-148° F.). The warmed water then flowsthrough the preheated water flow channel 18 into one of the two internalchambers of the second heat exchanger 20. In the second heat exchanger20, the water absorbs additional heat from the hot air flowing throughthe other internal chamber of the heat exchanger 20. This causes thewater temperature to rise even further, to a pasteurization level (e.g.,preferably 150-170° F., more preferably at least 160° F., and even morepreferably 160-161° F.). The pasteurized water then flows through thepasteurized water flow channel 22 into the residence tank 24. It will beappreciated that the residence tank 24 can be omitted from the design ormoved downstream of the output water flow channel 28, to serve as alater-stage collection tank. The pasteurized water continues through thepasteurized water flow channel 26 into the internal chamber of the firstheat exchanger 16 that does not contain the incoming wastewater effluent12 from the wastewater input flow channel 14. As explained above, thehot pasteurized water loses heat to the cooler wastewater 12, causingthe pasteurized water temperature to drop, preferably back toapproximately room temperature (e.g., 76° F.). The cooled pasteurizedwater exits the first heat exchanger 16 via the clean water output flowchannel 28, as clean output water 30.

[0040] It will also be appreciated that there is preferably provided aflow controller for controlling the rate of water flow through thesecond heat exchanger 20. Preferably, the water flow through the secondheat exchanger 20 is controlled so that the water absorbs sufficientheat from the turbine exhaust airflow to rise in temperature to a waterpasteurization temperature, for a time period sufficient to pasteurizethe water.

[0041] In one preferred embodiment, the natural gas fuel from the gasfuel source 42 and in the uncompressed gas flow channel 44 is atapproximately 100 psig and provides about 7.1 MMBtu/hr of power. Afterthe gas is pressurized in the gas compressor 46, it is preferably atapproximately 318 psig and provides about 74.6 MMBtu/hr of power. In oneembodiment, the turbine generator 61 is the TAURUS 70-T10301S, sold bySolar Turbines of San Diego, Calif. At an elevation of 200 feet abovesea level, ambient temperature of 59° F., and humidity of 60%, thisparticular turbine generator has a gross power output of 7.160 MW. Underall of these conditions, the turbine exhaust air in the airflow channel62 has a flow rate of about 210,044 lb/hr and a temperature of about916° F. Preferably, the additional heat imparted to the air in theductburner 64 from the natural gas in the uncompressed gas flow channel44 brings the air temperature to about 1034° F. In the preferredembodiment, the cooled air exiting the second heat exchanger 20 has atemperature of about 250° F. and flows at about 210,385 lb/hr out of thestack 70.

[0042] In this preferred embodiment, the heat exchangers 16 and 20 andthe residence tank 24 are sized and configured to pasteurize about 10million gallons of wastewater effluent 12 per day. In another preferredembodiment, the system is sized and configured to pasteurize twice thatamount per day. The skilled artisan will appreciate that the capacity ofthe system 5 can be adjusted by varying the sizes and heat transferqualities of the heat exchangers 16 and 20, by varying the sizes of theresidence tank 24 and the water flow channels, by selection of differentnatural gas fuels with different heating capacities, and/or by selectionof different turbine generators 61 with different turbine exhaustairflow characteristics. In preferred embodiments, the heat exchangersare configured to pasteurize preferably at least 5 million, morepreferably at least 10 million, more preferably at least 15 million, andeven more preferably at least 20 million gallons of wastewater per day.

[0043] In preferred embodiments, the water remains at the pasteurizationtemperature for preferably at least 2 seconds, more preferably at least5 seconds, more preferably at least 10 seconds, and even more preferablyat least 15 seconds. Generally, the hotter the water temperature theless time is required for pasteurization. Pasteurization of the water ata temperature of at least 160° F. for at least five seconds ispreferred. At 200° F., a pasteurization time of at least two seconds ispreferred. The water pasteurization temperature (i.e., the temperatureof the water in the water flow channel 22) is preferably 150-212° F. andmore preferably 155-200° F. Pasteurization in the range of 150-170° F.is desirable because higher temperatures would require greater heatgeneration from the power generation subsystem 8, which would in turnincrease costs and/or decrease the rate of production. The waterpasteurization temperature is preferably at least 160° F.

[0044] It is expected that the present invention will have particularadvantage and utility at the city level. The invention permitsmunicipalities to produce power and pasteurize water locally in acost-effective manner. The power generated can supplement powerpurchased from larger power companies. The pasteurized water can be usedfor local purposes. As used at a local or city level, the turbine 56 ofthe water pasteurization and power generation system 5 is preferably ofa relatively smaller size. In one embodiment, the turbine 56 is capableof producing up to 50 MW of power, and more preferably up to 1000 MW ofpower. In one preferred embodiment, the water pasteurization and powergeneration system 5 is capable of treating about 200,000 gallons ofwater per megawatt of power generated. The system 5 is preferablycapable of treating preferably at least 100,000 gallons/MW and morepreferably at least 500,000 gallons/MW of power generated. The system 5is most preferably capable of treating 200,000-1,500,000 gallons/MW ofpower generated. In one preferred embodiment, the system is capable oftreating 1.4 million gallons/MW of power generated.

[0045] The skilled artisan will appreciate that it is not necessary forthe water pasteurization subsystem 6 to include two heat exchangers astaught herein. For example, the wastewater 12 could be pasteurized byuse of a single heat exchanger receiving the turbine exhaust airflow(e.g., eliminate the first heat exchanger 16 and introduce thewastewater 12 directly into the second heat exchanger 20). However, twoheat exchangers are preferred because it increases the pasteurizationcapacity of the subsystem 6 significantly. If a single heat exchanger isused, it must raise the temperature of the wastewater 12 from at or nearroom temperature to at least the pasteurization temperature of 150-170°F., an increase of about 100° F. In order to increase the watertemperature this much, the water flow rate through the single heatexchanger must be limited, so that the water absorbs enough heat fromthe turbine exhaust airflow. In the single heat exchanger configuration,it is estimated that the system 5 can pasteurize 250,000 gallons ofwater per megawatt of power generated. However, by utilizing two heatexchangers 16, 20 as illustrated, it is possible for the first heatexchanger 16 to preheat the wastewater 12 to approximately 140° F. Thus,the second heat exchanger 20 only needs to increase the watertemperature by 10-31° F. (preferably up to 150-171° F., more preferablyup to 160-161° F.). This permits a higher water flow rate. It isestimated that with two heat exchangers the system 5 can pasteurize 1.4million gallons of water per megawatt of power generated. Anotherbenefit of using two heat exchangers is that the pasteurized waterbecomes cooled to near room temperature. While the illustratedembodiment utilizes two heat exchangers, the skilled artisan willappreciate that the system 5 can include any number of heat exchangersconnected in series in the manner shown in FIG. 1.

[0046] While the illustrated embodiment utilizes natural gas to heat upthe air flowing into and exiting the turbine generator, it will beappreciated that the benefits of the invention can also be obtained byusing alternative sources of heat generation, such as nuclear energy orburning coal. It will be appreciated that any of a variety of differentforms of energy can be used to heat up the air flowing into and exitingthe turbine generator.

[0047] With continued reference to FIG. 1, the water pasteurization andpower generation system 5 can utilize so-called “digester gas” frompreheated and oxidized wastewater as a source of fuel for heating theworking fluid of the power generation subsystem 8. Preferably, thewastewater 12 is preheated and oxidized prior to entering the first heatexchanger 16. The preheating and oxidation promotes the growth ofbacteria and causes the wastewater to release digester gas, typicallymethane gas. When ignited, the digester gas is capable of impartingadditional heat to the working fluid.

[0048]FIG. 3 shows one embodiment of a system of the invention utilizingdigester gas as an additional heat source for the working fluid of thepower generation subsystem, wherein the digester gas is sent to theductburner 64. The wastewater 12 is preliminarily collected in a chamberor tank 95. As mentioned above, the wastewater 12 is preheated and/oroxidized to effect the release of digester gas into a digester gas flowchannel 96 that is connected to a gas compressor 97. Compression of thedigester gas is desirable in order to raise the heat production capacityof the digester gas, preferably to a level compatible with that of thenatural gas 42 in the preferred embodiment. After the digester gas iscompressed within the compressor 97, it flows through a digester gasflow channel 98 into the ductburner 64, where it mixes with the naturalgas 42 from the natural gas flow channel 44, in the preferredembodiment. In an alternative embodiment, the compressor 97 is omittedfrom the design, preferably with a single unobstructed digester gas flowchannel from the tank 95 to the ductburner 64.

[0049]FIG. 4 shows another embodiment that utilizes digester gas as anadditional heat source for the working fluid of the power generationsubsystem, wherein the digester gas mixes directly with the natural gasfuel source 42 of the preferred embodiment. The digester gas flows fromthe tank 95 through a digester gas flow channel 99 and into a gascompressor 100. After the digester gas is compressed within thecompressor 100, it flows through a digester gas flow channel 101directly into the natural gas source 42 in the preferred embodiment. Inthis embodiment, the digester gas mixes with the working fluid upstreamof the turbine 56. In some cases, the introduction of digester gas intothe turbine 56 may present a risk of turbine damage and/or may degradeturbine performance, in which case the embodiment of FIG. 3 is morepreferable to that of FIG. 4. However, when there is no risk of thedigester gas damaging the turbine (or when such risk is negligible), theembodiment of FIG. 4 may be preferred in some cases. In an alternativeembodiment, the compressor 100 is omitted from the design, preferablywith a single unobstructed digester gas flow channel from the tank 95 tothe natural gas fuel source 42 of the preferred embodiment.

[0050] Although this invention has been disclosed in the context ofcertain preferred embodiments and examples, it will be understood bythose skilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. Further, the various features of this invention can be usedalone, or in combination with other features of this invention otherthan as expressly described above. Thus, it is intended that the scopeof the present invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

What is claimed is:
 1. A system for producing power and pasteurizingwater, comprising: a turbine configured to receive a flow of a workingfluid, the working fluid flow configured to rotate blades and an outputshaft of the turbine; a power generator coupled to the turbine outputshaft and configured to convert rotation of the output shaft into power;a heat exchanger having first and second internal chambers, the firstchamber configured to receive working fluid exiting the turbine, thesecond chamber configured to receive water, the chambers configured topermit heat exchange between working fluid within the first chamber andwater within the second chamber to raise the temperature of water in thesecond chamber to at least a water pasteurization temperature; and aheat source operatively connected to impart heat to working fluidflowing through the turbine and the first chamber of the heat exchanger.2. The system of claim 1, wherein the working fluid comprises air. 3.The system of claim 1, wherein the water pasteurization temperature is150-170° F.
 4. The system of claim 1, wherein the water pasteurizationtemperature is at least 160° F.
 5. The system of claim 1, wherein thesystem is capable of pasteurizing at least 200,000 gallons of water permegawatt of power generated.
 6. The system of claim 1, wherein thesystem is capable of pasteurizing at least 500,000 gallons of water permegawatt of power generated.
 7. The system of claim 1, wherein thesystem is configured so that the heat source imparts heat to workingfluid upstream of and flowing into the turbine.
 8. The system of claim1, wherein the system is configured so that the heat source imparts heatto working fluid downstream of and flowing out of the turbine.
 9. Thesystem of claim 1, wherein the power generator is configured to convertrotation of the output shaft into electric power.
 10. The system ofclaim 1, wherein the heat source comprises a natural gas fuel source.11. The system of claim 10, wherein the natural gas fuel source is oneselected from the group consisting of methane, propane, and butane. 12.The system of claim 10, further comprising: a gas compressor having aninput and an output, the input of the gas compressor being connected toan output of the natural gas fuel source, the gas compressor configuredto compress natural gas received from the natural gas fuel source andpermit the compressed natural gas to flow through the output of the gascompressor; and a natural gas ignition chamber having a natural gasinput connected to the output of the gas compressor and a working fluidinput configured to receive working fluid, the natural gas ignitionchamber having an output connected to an input of the turbine, thenatural gas ignition chamber including a natural gas igniter forigniting the natural gas fuel to impart heat to working fluid within thenatural gas ignition chamber.
 13. The system of claim 12, wherein thenatural gas igniter of the natural gas ignition chamber comprises one ofan electric spark generator and a flame generator.
 14. The system ofclaim 12, further comprising an additional natural gas ignition chamberhaving a first input connected to the natural gas fuel source and asecond input connected to an output of the turbine, the additionalnatural gas ignition chamber having an output connected to the firstchamber of the heat exchanger, the additional natural gas ignitionchamber including a natural gas igniter for igniting the natural gasfuel to impart heat to working fluid within the additional natural gasignition chamber.
 15. The system of claim 14, wherein the additionalnatural gas ignition chamber comprises a ductburner.
 16. The system ofclaim 1, wherein the heat source comprises coal.
 17. The system of claim1, wherein the heat source comprises nuclear energy.
 18. The system ofclaim 1, wherein the heat exchanger is a second heat exchanger, thesystem further comprising a first heat exchanger having first and secondfluidly separate internal chambers, the chambers of the first heatexchanger configured to permit heat exchange between water within thefirst chamber of the first heat exchanger and water within the secondchamber of the first heat exchanger, the first chamber of the first heatexchanger having an input configured to receive wastewater and an outputconnected to an input of the second chamber of the second heatexchanger, the second chamber of the first heat exchanger having aninput connected to receive water expelled from an output of the secondchamber of the second heat exchanger, the second chamber of the firstheat exchanger also having an output configured to expel water.
 19. Thesystem of claim 1, wherein the first chamber of the heat exchanger hasan input configured to receive working fluid exiting the turbine and anoutput configured to expel the working fluid into the environment. 20.The system of claim 19, further comprising catalysts for cleaningworking fluid within the first chamber of the heat exchanger so that thequality of the working fluid in the first chamber of the heat exchangerconforms to emissions standards.
 21. The system of claim 20, wherein thecatalysts comprise one or both of CO and SCR.
 22. The system of claim19, further comprising a continuous emissions monitoring system formonitoring the quality of working fluid expelled from the output of thefirst chamber of the heat exchanger.
 23. A system for producing electricpower and pasteurizing water, comprising: a turbine power generatorconfigured to convert a flow of working fluid into electric power; and aheat exchanger having first and second fluidly separate internalchambers, the first internal chamber configured to receive an exhaustflow of working fluid from the turbine generator, the second internalchamber configured to receive water, the chambers configured to permitheat exchange between working fluid within the first chamber and waterwithin the second chamber to pasteurize water within the second chamber.24. The system of claim 23, further comprising a heat source configuredto impart heat to working fluid flowing into the turbine generator. 25.A system for producing power and pasteurizing water, comprising: aturbine configured to receive a flow of a working fluid, the workingfluid flow configured to rotate blades and an output shaft of theturbine; a power generator coupled to the turbine output shaft andconfigured to convert rotation of the output shaft into power; a heatexchanger having first and second internal chambers, the first chamberconfigured to receive working fluid exiting the turbine, the secondchamber configured to receive water, the chambers configured to permitheat exchange between working fluid within the first chamber and waterwithin the second chamber; and a heat source configured to impart heatto working fluid flowing through the turbine and the first chamber ofthe heat exchanger.
 26. The system of claim 25, wherein the heat sourceis configured to impart sufficient heat to the working fluid flowingthrough the turbine and the first chamber of the heat exchanger so thatthe working fluid is hot enough to raise the temperature of waterflowing through the second chamber of the heat exchanger to at least awater pasteurization temperature.
 27. A system for producing electricpower and pasteurizing water, comprising: a turbine power generatorconfigured to convert a flow of working fluid into electric power; and aheat exchanger having first and second fluidly separate internalchambers, the first internal chamber configured to receive an exhaustflow of working fluid from the turbine generator, the second internalchamber configured to receive water, the chambers configured to permitheat exchange between working fluid within the first chamber and waterwithin the second chamber.
 28. A method of producing power andpasteurizing water, comprising: causing a working fluid to flow througha turbine power generator, the flow of working fluid causing the turbinepower generator to generate power; after the working fluid exits theturbine power generator, directing the working fluid into a first of twofluidly separate internal chambers of a heat exchanger, the chambersconfigured to permit heat exchange between the working fluid within thefirst chamber and water within a second of the two chambers, the workingfluid within the first chamber being at a temperature greater than awater pasteurization temperature; causing water to flow through thesecond chamber of the heat exchanger, the water initially being colderthan the water pasteurization temperature; permitting the water flowingthrough the second chamber to absorb heat from the working fluid withinthe first chamber; and controlling the flow rate of the water flowingthrough the second chamber of the heat exchanger so that the watertemperature rises to at least the pasteurization temperature.
 29. Themethod of claim 28, further comprising heating the working fluid beforeit flows into the turbine power generator.
 30. The method of claim 29,wherein heating the working fluid comprises mixing the working fluidwith ignited natural gas fuel.
 31. The method of claim 30, furthercomprising compressing the natural gas fuel inside a gas compressorprior to mixing the natural gas fuel with the working fluid.
 32. Themethod of claim 29, wherein heating the working fluid comprises causingthe working fluid to absorb heat from burning coal.
 33. The method ofclaim 29, wherein heating the working fluid comprises causing theworking fluid to absorb nuclear energy.
 34. The method of claim 28,further comprising heating the working fluid after it exits the turbinepower generator and before it enters the first chamber of the heatexchanger.
 35. The method of claim 28, wherein the heat exchanger is asecond heat exchanger, and wherein causing water to flow through thesecond chamber of the second heat exchanger comprises: causingunpasteurized water to flow through a first of two fluidly separateinternal chambers of a first heat exchanger, the chambers of the firstheat exchanger configured to permit heat exchange between theunpasteurized water within the first chamber of the first heat exchangerand water within a second of the two chambers of the first heatexchanger; permitting the unpasteurized water flowing through the firstchamber of the first heat exchanger to absorb heat from water within thesecond chamber of the first heat exchanger; causing the unpasteurizedwater within the first chamber of the first heat exchanger to flow fromthe first heat exchanger into the second chamber of the second heatexchanger; permitting the water within the second chamber of the secondheat exchanger to absorb heat from the working fluid within the firstchamber of the second heat exchanger, so that the water within thesecond chamber of the second heat exchanger is brought to thepasteurization temperature; and causing the water at the pasteurizationtemperature to exit the second chamber of the second heat exchanger andflow through the second chamber of the first heat exchanger.
 36. Themethod of claim 28, wherein the pasteurization temperature is 150-170°F.
 37. The method of claim 28, wherein the pasteurization temperature isat least 160° F.
 38. The method of claim 28, further comprising causingthe water flowing through the second chamber of the heat exchanger toremain at a temperature of at least 160° F. for at least five seconds.39. The method of claim 28, further comprising pasteurizing at least200,000 gallons of water per megawatt of power generated.
 40. The methodof claim 28, further comprising pasteurizing at least 500,000 gallons ofwater per megawatt of power generated.
 41. The method of claim 28,further comprising: heating and oxidizing the water before it flowsthrough the second chamber of the heat exchanger so that the waterreleases digester gas; causing the digester gas to mix with the workingfluid; and igniting the digester gas in the presence of the workingfluid so that the digester gas imparts heat to the working fluid. 42.The method of claim 41, further comprising mixing the digester gas withnatural gas prior to said step of causing the digester gas to mix withthe working fluid.
 43. The method of claim 41, further comprisingcompressing the digester gas prior to said step of causing the digestergas to mix with the working fluid.
 44. A method of producing electricpower and pasteurizing water, comprising: pumping air through a turbinepower generator, the air causing the turbine power generator to generateelectric power; and after the air exits the turbine power generator,transferring heat from the air to water to raise the water temperatureto at least a water pasteurization temperature.